Hyolitha

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Hyolitha
Temporal range: Fortunian to end Permian, 536–251.9  Ma [1] [2] [3]
Hyoliths01.JPG
Hyolithes cerops, Spence Shale, Idaho (Middle Cambrian)
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Superphylum: Lophotrochozoa
Class:† Hyolitha
Marek, 1963
Orders

See text.

Hyoliths are animals with small conical shells, known as fossils from the Palaeozoic era. They are at least considered as lophotrochozoan, and possibly being lophophorates, a group which includes the brachiopods, while others consider them as being basal lophotrochozoans, or even molluscs. [4] [5] [6]

Contents

Morphology

The shell of a hyolith is typically one to four centimeters in length, triangular or elliptical in cross section. Some species have rings or stripes. It comprises two parts: the main conical shell (previously referred to as a ‘conch’) and a cap-like operculum. Some also had two curved supports known as helens [4] They are calcareous – probably aragonitic [7] All of these structures grew by marginal accretion.

Shell microstructure

The orthothecid shell has an internal layer with a microstructure of transverse bundles, and an external layer comprising longitudinal bundles. [7]

Helens

Some hyoliths had helens, long structures that taper as they coil gently in a logarithmic spiral in a ventral direction. [7] [4] The helens had an organic-rich central core surrounded by concentric laminae of calcite. They grew by the addition of new material at their base, on the cavity side, leaving growth lines. [7]

They were originally described by Walcott as separate fossils under the genus name Helenia, (Walcott's wife was named Helena and his daughter Helen); Bruce Runnegar adopted the name helen when they were recognized as part of the hyolith organism. [7] Encrusting organisms have been found on helens, and also on both sides of the main shell, all of which are therefore supposed to have been raised above the sea bed. The helens have been interpreted as props that supported the feeding organ, the lophophore, above the sea bed. [4]

Operculum

The operculum closes over the aperture of the shell, leaving (in hyolithids) two gaps through which the helens can protrude. [7] It comprises two parts: the cardinal shield, a flat region at the top of the shell; and the conical shield, the bottom part, which is more conical. [7] The inside of the shell[ the inside of the operculum? ] bears a number of protrusions, notably the dorsal cardinal processes and the radially-arranged clavicles. [7]

Reconstruction of Haplophrentis, hyolith with known soft tissue Haplophrentis.png
Reconstruction of Haplophrentis , hyolith with known soft tissue

Soft tissues

The soft tissues of the mid-Cambrian hyolith Haplophrentis, from the Burgess Shale and Spence Shale Lagerstätten include a gullwing-shaped band below the operculum. This band is interpreted as a lophophore, a feeding organ with a central mouth; it bears 12 to 16 tentacles. From the mouth a muscular pharynx leads to a gut, which loops back and exits beyond the crown of tentacles. Next to the gut are a pair of large kidney-shaped organs of uncertain nature. Under the operculum are muscles. The thin body wall circumscribes the interior of the shell, except the apex. [4] Preserved intestines have been described from the Ordovician hyolith Girvanolithes thraivensis. [8]

Taxonomy

Hyoliths from the Middle Ordovician of northern Estonia; these are internal molds. Hyoliths02.JPG
Hyoliths from the Middle Ordovician of northern Estonia; these are internal molds.

The hyoliths are divided into two orders, the Hyolithida and the Orthothecida.

Hyolitha have dorso-ventrally differentiated opercula, with the ventral surface of the shell extending forwards to form a shelf termed the ligula. [7]

The Orthothecida are somewhat more problematic, and probably contain a number of non-hyoliths simply because they are so difficult to identify with confidence, especially if their operculum is absent. [7] They have a straight (planar) opening, sometimes with a notch on the bottom side, and sealed with an operculum that has no ligula, clavicles, furrow or rooflets. [9]

Hyptiotheca is an unusual hyolithid, in that it lacks clavicles. [9]

Orthothecids fall into two groups: one, the orthothecida sensu stricto, [10] is kidney or heart shaped in cross-section due to a longitudinal groove on its ventral surface, and its opercula bear cardinal processes; the other has a rounded cross-section and often lacks cardinal processes, making them difficult to distinguish from other cornet-shaped calcareous organisms. [9] All were sessile and benthic; some may have been filter feeders. [10]

Phylogenetic position

Haplophrentis carinatus from the Stephen Formation, Burgess Shale (Middle Cambrian), Burgess Pass, British Columbia, Canada. Haplophrentis Burgess Shale.jpg
Haplophrentis carinatus from the Stephen Formation, Burgess Shale (Middle Cambrian), Burgess Pass, British Columbia, Canada.

Because hyoliths are extinct and do not obviously resemble any extant group, it has long been unclear which living group they are most closely related to. They have been supposed to be molluscs; or to belong to their own phylum in an unspecified part of the tree of life. [11] Their grade of organization was historically considered to be of the 'mollusc-annelid-sipunculid' level, [12] consistent with a Lophotrochozoan affinity, and comparison was primarily drawn with the molluscs or sipunculids. [12] [13] Older studies (predating the Lophotrochozoan concept) consider hyoliths to represent a stem lineage of the clade containing (Mollusca + Annelida + Arthropoda). [3]

A secure classification at last became possible in 2017, on the basis of Burgess Shale specimens that preserve lophophores. This diagnostic characteristic demonstrates an affinity with the Lophophorata, a group that contains Brachiopoda, Bryozoa (perhaps), and Phoronida. [4]

A study in 2019 estimated that hyoliths are more likely to be basal members of the lophotrochozoans rather than lophophorates. [5] Meanwhile, a study in 2020 instead concluded that hyoliths belong to Mollusca, [14] as did a different study in 2022. [6]

Ecology

Hyolithids were benthic (bottom-dwellers), using their helens as stilts to hold the opening of their shells above the sea floor. [4] Orthothecids did not have helens, but are presumed to have been sessile and benthic.

In the Cambrian, their global distribution shows no sign of provinciality, suggesting a long-lived planktonic larval life stage (reflected by their protoconchs); but by the Ordovician distinct assemblages were becoming evident. [9]

Some orthothecids are preserved in vertical [life] orientation, suggesting a sessile suspension-feeding habit; hyolithids tend to be flat on the bottom, and their shape and the occurrence of epibionts are consistent with a sessile suspension feeding habit via orientation relative to passive currents. [15]

Occurrence

The first hyolith fossils appeared about 540  million years ago in the Purella antiqua Zone of the Nemakit-Daldynian Stage of Siberia and in its analogue the Paragloborilus subglobosus–Purella squamulosa Zone of the Meishucunian Stage of China. Hyolith abundance and diversity attain a maximum in the Cambrian, followed by a progressive decline up to their Permian extinction. [2] [16]

Similar organisms

Due to the simple shape of their shell, hyoliths have been something of a wastebasket taxon, and organisms originally interpreted as hyoliths have sometimes later been recognized as something else – as for example in the case of the cnidarian-like Glossolites [17] and Palaeoconotuba. [18]

See also

Related Research Articles

<span class="mw-page-title-main">Lophophore</span>

The lophophore is a characteristic feeding organ possessed by four major groups of animals: the Brachiopoda, Bryozoa, Hyolitha, and Phoronida, which collectively constitute the protostome group Lophophorata. All lophophores are found in aquatic organisms.

<span class="mw-page-title-main">Halkieriid</span> Family of incertae sedis

The halkieriids are a group of fossil organisms from the Lower to Middle Cambrian. Their eponymous genus is Halkieria, which has been found on almost every continent in Lower to Mid Cambrian deposits, forming a large component of the small shelly fossil assemblages. The best known species is Halkieria evangelista, from the North Greenland Sirius Passet Lagerstätte, in which complete specimens were collected on an expedition in 1989. The fossils were described by Simon Conway Morris and John Peel in a short paper in 1990 in the journal Nature. Later a more thorough description was undertaken in 1995 in the journal Philosophical Transactions of the Royal Society of London and wider evolutionary implications were posed.

<span class="mw-page-title-main">Evolution of molluscs</span> The origin and diversification of molluscs through geologic time

The evolution of the molluscs is the way in which the Mollusca, one of the largest groups of invertebrate animals, evolved. This phylum includes gastropods, bivalves, scaphopods, cephalopods, and several other groups. The fossil record of mollusks is relatively complete, and they are well represented in most fossil-bearing marine strata. Very early organisms which have dubiously been compared to molluscs include Kimberella and Odontogriphus.

<i>Haplophrentis</i> Extinct genus of Cambrian organisms

Haplophrentis is a genus of tiny shelled hyolithid which lived in the Cambrian Period. Its shell was long and conical, with the open end protected by an operculum, from which two fleshy arms called helens protruded at the sides. These arms served to elevate the opening of the shells above the sea floor, acting like stilts.

<i>Yochelcionella</i> Extinct genus of molluscs

Yochelcionella is an extinct genus of basal molluscs which lived during the Tommotian epoch, the first epoch of the Cambrian period. This genus is often reconstructed to resemble snails.

<span class="mw-page-title-main">Helcionellid</span> Extinct order of molluscs

Helcionellid or Helcionelliformes is an order of small fossil shells that are universally interpreted as molluscs, though no sources spell out why this taxonomic interpretation is preferred. These animals are first found about 540 to 530 million years ago in the late Nemakit-Daldynian age, which is the earliest part of the Cambrian period. A single species persisted to the Early Ordovician. These fossils are component of the small shelly fossils (SSF) assemblages.

<span class="mw-page-title-main">Phoronid</span> Phylum of marine animals, horseshoe worms

Phoronids are a small phylum of marine animals that filter-feed with a lophophore, and build upright tubes of chitin to support and protect their soft bodies. They live in most of the oceans and seas, including the Arctic Ocean but excluding the Antarctic Ocean, and between the intertidal zone and about 400 meters down. Most adult phoronids are 2 cm long and about 1.5 mm wide, although the largest are 50 cm long.

<span class="mw-page-title-main">Tommotiid</span> Extinct order of brachiopods

Tommotiids are an extinct group of Cambrian invertebrates thought to be early lophophorates.

<span class="mw-page-title-main">Evolution of brachiopods</span> The origin and diversification of brachiopods through geologic time

The origin of the brachiopods is uncertain; they either arose from reduction of a multi-plated tubular organism, or from the folding of a slug-like organism with a protective shell on either end. Since their Cambrian origin, the phylum rose to a Palaeozoic dominance, but dwindled during the Mesozoic.

Stenothecidae is an extinct family of fossil univalved Cambrian molluscs which may be either gastropods or monoplacophorans.

Anabarella is a species of bilaterally-flattened monoplacophoran mollusc, with a morphological similarity to the rostroconchs. Its shell preserves evidence of three mineralogical textures on its outer surface: it is polygonal near the crest of the shell, subsequently changing to both spiny and stepwise. Its internal microstructure is calcitic and semi-nacreous. Its name reflects its provenance from Anabar, Siberia. It has been interpreted as ancestral to the rostroconchs, and has been aligned to the Helcionellidae.

<i>Fordilla</i> Extinct genus of bivalves

Fordilla is an extinct genus of early bivalves, one of two genera in the extinct family Fordillidae. The genus is known solely from Early Cambrian fossils found in North America, Greenland, Europe, the Middle East, and Asia. The genus currently contains three described species, Fordilla germanica, Fordilla sibirica, and the type species Fordilla troyensis.

The cephalopods have a long geological history, with the first nautiloids found in late Cambrian strata, and purported stem-group representatives present in the earliest Cambrian lagerstätten.

Stenothecoida is a taxon of bivalved fossils from the Early to middle Cambrian period. They look a bit like brachiopods or bivalve molluscs.

Watsonella is an extinct genus of mollusc known from early (Terreneuvian) Cambrian strata. It has been hypothesized to be close to the origin of bivalves. It contains a single species, Watsonella crosbyi.

The orthothecids are one of the two hyolith orders.

<span class="mw-page-title-main">Hyolithida</span> Extinct order of molluscs

The Hyolithida are lophophorates, one of the two orders of hyolithid, the other being the Orthothecida. Most of our knowledge of the hyolithids comes from studies on the Hyolithida. Both orders had an operculum that was not hinged to the conch. However, the Hyolithida are distinct from the Orthothecida in having additional paired, curved, whiskerlike appendages. The Hyolithida were probably bottom feeders living in shallow water, and had tentacules.

Hyolithellus is a conical tubular fossil from the Cambrian, originally considered a hyolith but since reinterpreted tentatively as an annelid worm.

Cupitheca is a genus of Cambrian hyolith with the unusual distinction of shedding the apex of its camerate conical shell. As with Triplicatella and Hyptiotheca, its designation to the hyolithids or orthothecids is not straightforward, exhibiting as it does a mixture of the characters that would normally demark the two subtaxa of Hyolitha.

References

  1. ↑ Kouchinsky, A.; Bengtson, S.; Runnegar, B.; Skovsted, C.; Steiner, M.; Vendrasco, M. (March 2012). "Chronology of early Cambrian biomineralization". Geological Magazine. 149 (2): 221–251. Bibcode:2012GeoM..149..221K. doi: 10.1017/S0016756811000720 .
  2. 1 2 Malinky, J. M. (2009). "Permian Hyolithida from Australia: The Last of the Hyoliths?". Journal of Paleontology. 83: 147–152. doi:10.1666/08-094R.1.
  3. 1 2 Runnegar, Bruce; Pojeta, John; Morris, Noel J.; Taylor, John D.; Taylor, Michael E.; McClung, Graham (1975). "Biology of the Hyolitha". Lethaia. 8 (2): 181. doi:10.1111/j.1502-3931.1975.tb01311.x.
  4. 1 2 3 4 5 6 7 Moysiuk, Joseph; Smith, Martin R.; Caron, Jean-Bernard (11 January 2017). "Hyoliths are Palaeozoic lophophorates" (PDF). Nature. 541 (7637): 394–397. Bibcode:2017Natur.541..394M. doi:10.1038/nature20804. PMID   28077871. S2CID   4409157. Archived (PDF) from the original on 9 October 2022.
  5. 1 2 Liu, Fan; Skovsted, Christian B; Topper, Timothy P; Zhang, Zhifei; Shu, Degan (1 February 2020). "Are hyoliths Palaeozoic lophophorates?". National Science Review. 7 (2): 453–469. doi:10.1093/nsr/nwz161. ISSN   2095-5138. PMC   8289160 . PMID   34692060.
  6. 1 2 Li, Luoyang; Skovsted, Christian B.; Topper, Timothy (August 2022). "Deep origin of the crossed‐lamellar microstructure in early Cambrian molluscs". Palaeontology . 65 (4). doi:10.1111/pala.12620. S2CID   251866827 . Retrieved 25 November 2022.
  7. 1 2 3 4 5 6 7 8 9 10 Mus, M. Martí; Bergström, J. (September 2007). "Skeletal Microstructure of Helens, Lateral Spines of Hyolithids". Palaeontology. 50 (5): 1231–1243. doi: 10.1111/j.1475-4983.2007.00700.x .
  8. ↑ Malinky, John M. (July 2003). "Ordovician and Silurian hyoliths and gastropods reassigned from the Hyolitha from the Girvan district, Scotland". Journal of Paleontology . 77 (4): 625–645. doi:10.1666/0022-3360(2003)077<0625:oashag>2.0.co;2 . Retrieved 26 November 2022.
  9. 1 2 3 4 Malinky, J.M.; Skovsted, C.B. (2004). "Hyoliths and small shelly fossils from the Lower Cambrian of North−East Greenland". Acta Palaeontologica Polonica. 49 (4): 551–578.
  10. 1 2 Malinky, J. M. (2009). "First Occurrence of Orthotheca Novák, 1886 (Hyolitha, Early Devonian) in North America". Journal of Paleontology. 83 (4): 588–596. doi:10.1666/08-164R.1. S2CID   130227630.
  11. ↑ Malinky, John M. (2009). "Permian Hyolithida from Australia: The Last of the Hyoliths?". Journal of Paleontology. 83 (1): 147–152. doi:10.1666/08-094R.1. JSTOR   29739075.
  12. 1 2 Runnegar, B. (January 1980). "Hyolitha: Status of the phylum". Lethaia. 13: 21–25. doi:10.1111/j.1502-3931.1980.tb01025.x.
  13. ↑ Kouchinsky, A. V. (2000). "Skeletal microstructures of hyoliths from the Early Cambrian of Siberia". Alcheringa: An Australasian Journal of Palaeontology. 24 (2): 65–81. doi:10.1080/03115510008619525. S2CID   140660142.
  14. ↑ Li, Luoyang; Skovsted, Christian B.; Yun, Hao; Betts, Marissa J.; Zhang, Xingliang (26 August 2020). "New insight into the soft anatomy and shell microstructures of early Cambrian orthothecids (Hyolitha)". Proceedings of the Royal Society B: Biological Sciences. 287 (1933): 20201467. doi:10.1098/rspb.2020.1467. PMC   7482263 . PMID   32811320.
  15. ↑ Kouchinsky, A.V. (2000). "Mollusks, hyoliths, stenothecoids and coeloscleritophorans". In A. Yu. Zhuravlev; R. Riding (eds.). The Ecology of the Cambrian Radiation. The Critical Moments and Perspectives in Earth History and Paleobiology. Columbia University Press. pp. 326–349. doi:10.7312/zhur10612-015. ISBN   978-0231505161.
  16. ↑ Steiner, M.; Li, G.; Qian, Y.; Zhu, M.; Erdtmann, B. D. (2007). "Neoproterozoic to Early Cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the Yangtze Platform (China)". Palaeogeography, Palaeoclimatology, Palaeoecology. 254 (1–2): 67. Bibcode:2007PPP...254...67S. doi:10.1016/j.palaeo.2007.03.046.
  17. ↑ Sun, Haijing; Zhao, Fangchen; Zhu, Maoyan (2022). "Anatomy, palaeoautecology and phylogenetic affinity of tubular Glossolites magnus from the early Cambrian Chengjiang biota, South China". Papers in Palaeontology. 8 (6). doi:10.1002/spp2.1473. S2CID   255125977.
  18. ↑ Qu, Hanzhi; Li, Kexin; Ou, Qiang (2023). "Thecate stem medusozoans (Cnidaria) from the early Cambrian Chengjiang biota". Palaeontology. 66. doi: 10.1111/pala.12636 . S2CID   256562444.
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